Watt (W)

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Summary

The watt (W) is a symbol to describe power, or the rate at which a battery or device can transfer energy. It comes from the International System of Units (SI) – a modern form of the metric system.
In SI, the definition of watt is 1 joule per second.

• 1 watt = 1 joule per second
• 1 joule = 1 watt times one second

An electromagnetic joule can be measured by the energy dissipated as heat when (one amp of current flows through one ohm of resistance) for one second.

Lithium-ion battery Watt (W) Calculators

Calculating wattage is easy. For lithium-ion batteries and electronic devices, there are three electromagnetic watt formulas we can use, given that we know two other variables.

Volts & Amps

Enter ohms, and volts to calculate watts.

This electromagnetic formula calculates watts for electric devices like batteries. It says one watt (W) equals one amp (A) of current flowing through an electrical potential difference of one volt (V).

To boil it down – watts equals volts times amps. That’s why watts are sometimes called volt-amps.

Volts & Ohms

Enter ohms, and amps to calculate watts.

This way uses resistance and volts. In plain English, this formula says

Amps & Ohms

Enter amps and volts to calculate watts.

Conversions

Abbreviations

The femtowatt is equal to one quadrillionth (10−15) of a watt. Technologically important powers that are measured in femtowatts are typically found in reference(s) to radio and radar receivers.

For example, meaningful FM tuner performance figures for sensitivity, quieting and signal-to-noise require that the RF energy applied to the antenna input be specified. These input levels are often stated in dBf (decibels referenced to 1 femtowatt). This is 0.2739 microvolt across a 75-ohm load or 0.5477 microvolt across a 300-ohm load; the specification takes into account the RF input impedance of the tuner.

Possible confusion

Uses cases

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Related

Watt-hours